Large-scale deployment of fiber to the home (FTTH) is accompanied with an increase in bandwidth requirements of optical access. Currently, a PON (Passive Optical Network) technology is mainly used for optical access. The passive optical network (PON) technology is a point-to-multipoint fiber transmission and access technology. A broadcast manner is used downstream, and a time division multiple access (TDMA) manner is used upstream. A topology structure such as a tree type, a star type, or a bus type may be flexibly formed. No node device is required at an optical branch point, and only one simple optical splitter needs to be installed. FIG. 1 is a schematic diagram of a tree topology structure commonly used in an existing PON, including an optical line terminal (OLT) 101 on an office side, an optical network unit (ONU) or an optical network terminal (ONT) 103 on a user side, and an optical distribution network (ODN) 102. The “passive” means that the ODN does not include any active electronic component or electronic power supply, and includes only a passive component such as an optical splitter. In a PON system, transmission from an OLT to an ONU is a downstream direction, and transmission from an ONU to an OLT is an upstream direction.
At a current stage, there are various PON technologies, such as a GPON (Gigabit-Capable PON) and an EPON (Ethernet Passive Optical Network). For the current GPON or EPON network, when single-channel transmission exceeds 10 Gb/s, bandwidth efficiency of the GPON or EPON network is relatively low if non-return to zero (NRZ) code is still used. Further, in optical communications, when an NRZ encoding rate exceeds 10 Gb/s, dispersion of NRZ encoding becomes extremely serious. Therefore, after the single-channel transmission is higher than 10 Gb/s, a multi-order or higher-order modulation scheme is mostly used. Most common modulation schemes are PAM (Pulse Amplitude Modulation, pulse amplitude modulation) 4, duobinary modulation, quadrature phase shift keying (QPSK) modulation, orthogonal frequency division multiplexing (OFDM) modulation, and the like. When a system supports a plurality of modulation schemes, currently there is still no effective solution to how to register an ONU/ONT (Optical Network Terminal) and put the ONU/ONT online and switch a modulation scheme after registering the ONU/ONT and putting the ONU/ONT online.